Therearemultiplebehavioralmethodsofcontraception. Totalabstinenceisthebestwaytoavoidgettingpregnant.Othermethodsincludetherhythmmethod,whichreliesonabstinencefromsexualintercourseduringfertileperiodsaroundthetimeofovulation.Thefertileperiodextendsfrom3to4daysbeforethetimeofovulationuntil3to4daysafterward.Asecondmethodiswithdrawalbeforeejaculation,coitus interruptus. Boththesemethodshavehigherfailurerates(20%–30%)thanbarrier methods (2%–12%),intrauterine devices (IUDs) (<2%),andoral contraceptives (<1%)do.Barrierssuchascondoms ordiaphragms aremoreeffectivewhenusedwithspermicidal jellies. Ofallmethods,onlycondomsprovideeffectiveprotectionfromsexuallytransmitteddiseasesinsexuallyactiveindividuals.IUDsarerelativelyeffective.Theypreventimplantationbylocallyproducinganinflammatoryresponseintheendometrium.SomeformsofIUDscontaincopper,zinc,orprogestins,whichinhibitspermtransportorviabilityinthefemalereproductivetract.
OralcontraceptiveshavebeenmarketedintheUnitedStatessincetheearly1960s.Thedosesofsteroidsusedtodayaresignificantlylowerthanthoseused35yearsago.Properlyused,oralcontraceptiveshavealowfailurerate.Manyformsoforalcontraceptivesaremarketedtoday.Thetrendovertheyearshasbeentodecreasethedosageofsteroidsusedbecausethesideeffectsaredosedependent.Alloralsteroidalcontraceptivescontaineitheracombinationofanestrogenandaprogestinoraprogestinalone.Oralcontraceptivesworkthroughmultiplemechanisms.MostblocktheLHsurgethattriggersovulation.However,somepills(e.g.,progestin-onlyminipill)donotpreventLHsurges.Fertilityisalsoblockedbychangingthenatureofcervicalmucus,alteringendometrialdevelopment,orregulatingfallopiantubemotility.BecausethesecontraceptivessuppressFSH,theyimpairearlyfolliculardevelopment.
Emergency contraception involveshormonaltreatmentdesignedtoinhibitordelayovulation,inhibitcorpusluteumfunction,disruptthefunctionoftheoviductsanduterus,oranycombinationofthesemechanisms.Forexample,candidatesforemergencycontraceptionincludewomenwhoaresexuallyassaultedorwhoexperiencedfailureofabarriermethod(e.g.,rupturedcondom).Therearemorethan20typesofcommerciallyavailable“morning-after”pills.Thecurrentlypreferredmedicationislevonorgestrel (Plan B), whichisasyntheticprogestin-onlypill.Theefficacyofthepillisinverselycorrelatedwiththetimeitistakenafterintercourse.Theexactmechanismofactionisnotknown.Treatmenthasnoeffectifimplantationhasoccurred.
Medical(hormonal) termination ofpregnancy(abortion)canbeachievedupto49days’gestationbyadministrationofmifepristone (RU-486), aprogesteronereceptorantagonistthatinducescollapseofthepregnantendometrium.Mifepristoneisfollowed48hourslaterbyingestionorvaginalinsertionofasynthetic prostaglandin E (e.g.,misoprostol),whichinducesmyometrialcontractions.
alveolar and ductal lumens. Thus the nursing infant does not gain milk by applying negative pressure to the breast from suckling. Rather, milk is actively ejected through a neuroendocrine reflex. Oxytocin release and milk let-down can be induced by psychogenic stimuli such as the mother hearing a baby crying on television or thinking about her baby. Such psychogenic stimuli do not affect PRL release.